The present invention relates to a swash plate type compressor and, more particularly, to a piston joint of the same.
A conventional swash plate type compressor comprises a rotary shaft, a swash plate rotatable together with the rotary shaft, a reciprocatable piston, and a piston joint for coupling the piston with the swash plate. The piston joint usually includes a socket connected integral with the piston and a pair of shoes (for example, see Japanese Unexamined Patent Publications Nos. S61-135990, S49-65509, and S56-138474). The socket has concave surfaces opposite to each other. The swash plate is inserted between the concave surface of the socket. The shoes are interposed between the swash plate and the concave surfaces, respectively. Each of the shoes has a flat surface slidable relative to the swash plate and a convex surface opposite to the flat surface and slidable relative to the concave surface.
During the compressor is operative, the shoes wobble inside the socket of the piston in accordance with the rotation of the swash plate. Therefore, it is desired to keep sufficient lubrication between the convex surfaces of the shoes and the concave surfaces of the socket. Such lubrication can be attained by a mist of lubricating oil contained in refrigerant gas within the compressor being introduced between the convex surfaces of the shoes and the concave surfaces of the socket.
Conventionally, the convex surfaces of the shoes and the concave surfaces of the socket are designed to be substantially same to each other in radius of curvature (for example, see Japanese Unexamined Patent Publication No. H10-220354). With this structure, there is substantially no clearance between the convex surfaces of the shoes and the concave surfaces of the socket. Therefore, a mist of lubricating oil is hardly introduced between the convex surfaces of the shoes and the concave surfaces of the socket. This may affect the- retention of the sufficient lubrication between the convex surfaces of the shoes and the concave surfaces of the socket so as to wear the sliding surfaces to widen clearance.
It is therefore an object of the present invention to provide a swash plate type compressor in which lubricating oil can be sufficiently supplied between convex surfaces of shoes and concave surfaces of a socket.
Other objects of the present invention will become clear as the description proceeds.
According to the present invention, there is provided a swash plate type compressor which comprises a rotary shaft, a swash plate rotatable together with the rotary shaft, a piston, and a shoe interposed between the swash plate and the piston for converting the rotation of the swash plate into a reciprocating motion of the piston, the shoe having a spherically convex surface, the piston having a concave surface for receiving the spherically convex surface, the concave surface having a first and a second spherical surface which are adjacent to and offset from each other to make a slight step extending along the concave surface.